Coal has long been used as a source of fuel. As the search for alternative fuels increases, several inventors have been looking toward further developing technology related to the use of coal. These inventors have come to recognize that the natural gas found in coal is not limited to coal, but rather is found in various forms of man-made and naturally occurring substances including, but not limited to municipal solid waste, sewage, wood waste, biomass, paper, plastics, hazardous waste, tar, pitch, activated sludge, rubber tires and oil-based residue.
The question has generally not been where one should look for natural gas, but rather how to liberate the natural gas. This has led to several different confined gasification liquefaction techniques. These systems in general terms include the down draft gasification, updraft gasification, and fluidized bed gasification.
The down draft gasification, also called a “co-current configuration system”, relies on gravity to move the feedstock, which perhaps is coal. The ignition system flows with the feedstock with resultant ash or slag falling out the bottom. The ash or slag is hazardous waste and is treated as such. This system of partial combustion yields a low BTU gas that must undergo extensive cleaning.
The updraft gasification, also called a “countercurrent system”, uses a blower to direct the feedstock up through the system. The combustion source is generally directed in an opposite direction to the feedstock or perpendicular to it. The ash and slag falls out the bottom where it is collected as hazardous waste. This is a partial combustion system that results in low BTU gas and tars that must be cleaned prior to use.
The conventional fluidized bed uses sand, char or some combination thereof. The fluid, usually air or steam, is directed through the sand, to the feedstock thereabove. The environment is usually oxygen starved resulting in partial combustion. The temperatures are relatively low resulting in low BTU gas that must be extensively cleaned prior to use. The ash is corrosive, invoking the use of limestone to minimize the corrosive effect. Some examples of the fluidized bed technology follow:
Giglio (U.S. Patent Application 2006/0130401) discloses a method of co-producing activated carbon in a circulating fluidized bed gasification process. The carbonacious material is treated in a fluidized bed to form syngas and char. (¶14) In a subsequent step, the char is turned to activated carbon with steam and carbon dioxide. Giglio teaches using the activated carbon to clean the syngas and separation of the gas and activated carbon. The cleaned syngas and solids are separated in a dust. Giglio uses a separator to separate the activated carbon and natural gas from the feedstock. That is, the gaseous flows through the fluidized bed are not used to separate components of carbonacious material on the basis of density.
Jha et al. (U.S. Pat. No. 5,187,141) discloses a process for the manufacture of activated carbon from coal by mild gasification and hydrogenation. The coal is first heated to a temperature between evaporation of water and below removal of volitilization. The dry coal is the heated in a mostly non-oxygenous atmosphere to volatilize and remove the contained volatile matter and produce char. In a second step, the char is subjected to a hydrogenation process to activate the carbon. The gaseous flows through the fluidized bed are not used to separate components of carbonacious material on the basis of density.
Ueno et al. (United States Patent Application 2003/0027088) discloses a method for treating combustible wastes. Combustible wastes includes paper, plastics, coal, tar, pitch, activated sludge, and oil-based residue. ¶8. The combustible wastes are carbonized at a temperature of around 400-600 degrees C. The carbonized material is then subjected to a temperature around 1000-1300 degrees C. in an inert atmosphere. This drives off the volatiles and may activate the carbon. The carbonized product is blown into exhaust gas, e.g., volatiles, to purify the exhaust gas. (Exhaust gas is preferred to be from refuse incineration, electric power plants, steel-making electric furnace, scrap melting furnace, and sintering machine.). The volatiles are used as a heat source for the carbonization step, although they are acknowledged to have harmful substances contained therein. ¶40.
The rate of fluid flow has generally not been discussed nor has the benefits of the fluid flow rate been considered. What is needed is a flow rate of gas in fluidized bed during conversion of carbon based material to natural gas and activated carbon that yields beneficial results that extend beyond the speed of combustion or conversion. Desirably, the flow rate separates material desired to be suspended above the fluidized bed from the material not desired to be above the bed.